When Nazi Germany took over Austria in March 1938, there was an outburst of not just anti-Semitism but outright sadism against the Jews. They were, among much else, made to scrub the slogans of the previous regime off walls and pavements. Then the expropriations started. An elderly Jewish couple who lost their shop appealed to Hitler in Berlin. Did His Excellency the Chancellor, they wrote, perhaps remember that as a young painter before the war selling his paintings on the corner of the Siebensterngasse, he would when it rained drop in at a certain shop and be given a cup of tea? Could he now see his way to helping the people who had treated him with such kindness? Hitler marked that the letter should be ignored, and the old couple surely went to a death camp.

We owe our knowledge of this fact to a remarkable 1999 book: "Hitler's Vienna" by Brigitte Hamann. Her extensive research revealed that Hitler was not really an anti-Semite until after World War I. What had happened in those crucial wartime years is the question that Thomas Weber now answers in "Hitler's First War." Like Ms. Hamann, he has searched out original documents and found new material. Like her, he fundamentally alters our understanding of one of the most studied figures of the 20th century.

Hitler wrote about his war experiences in "Mein Kampf" (1925), and biographers have generally relied on his account. He put himself across as a soldier-hero: a "runner" carrying messages back and forth through machine-gun fire and artillery, twice decorated with the Iron Cross for bravery, wounded and then, toward the end of the war, blinded by poison gas. He learned of the end of the war at a military hospital in Pasewalk, not far from Berlin, and he wept.

In Hitler's version, the weeping soon turned vindictive against the soft-brained academics, Jews and members of the left who, he alleged, had caused Germany to lose the war. Remaining in the army, he was sent to Bavaria to fight against left-wing revolutionaries. (And yet Mr. Weber has discovered that, briefly at the turn of 1918-19, and unmentioned in "Mein Kampf," Hitler wore a red brassard and supported the short-lived Bavarian Soviet Republic.) Demobilized, he became an informer for the army's propaganda unit— though whether he volunteered or was coerced because of his short-lived involvement with the Bavarian Soviet Republic, Mr. Weber admits we cannot know—and was sent to monitor a meeting of the obscure German Workers' Party, soon to be re-named National Socialist German Workers' Party. Hitler was deeply impressed by the party's hypernationalism and anti-Semitism and joined within a week of attending his first meeting. He also found that he was a tremendously effective public speaker. The speeches do not translate: What sounds superb in one language can sound plain comic in another. But desperate Germans were soon paying to hear Hitler speak, and, as the party's chief source of revenue, he took over the leadership.

How did the young Hitler—diffident, gauche, without solid political convictions—turn into the fascist demagogue of 1922? There is no simple answer to this question, but "Hitler's First War" debunks some of the standard responses. Biographers have long assumed that the war marked a turning point: the comradeship of the trenches, the common soldier's hatred of the profiteers in the rear and the sense of betrayal with the peace made in 1918. Yet there was the nagging question of why the brave, decorated soldier of "Mein Kampf" was not promoted. Hitler served more or less for the whole of the war and never rose above the rank of corporal, which, given that he undoubtedly had leadership qualities, comes as a considerable surprise.

With some luck and a lot of diligence, Mr. Weber has discovered the missing documents of Hitler's war service, and it is fair to say that very little of Hitler's own account survives the discovery. There were indeed two Iron Crosses, but his regimental runner's job was not necessarily dangerous, and he lived in relative comfort at the regimental headquarters away from the front lines. Ordinary soldiers referred to such men as Etappenschweine ("rear pigs") —all armies have such a word: "cushy number" and "base wallah" are British examples. Officers had to dish out a quota of medals, and if you did not offend them they would just put your name on the list. Hitler was not, it appears, particularly courageous. He was just there. And, as it happens, a Jewish superior officer, Hugo Gutmann, recommended Hitler for his first Iron Cross. He was not thanked for this act in later life—though his fate, emigration to the United States, was greatly preferable to that of the old couple in Vienna.

There also wasn't much comradeship. When Hitler broke surface in politics, he asked his old comrades in the regiment for support and discovered that on the whole they had not liked him one bit. Men who had fought at the front in World War I were, moreover, not at all keen on staging a second war, and extraordinarily few of Hitler's old comrades went along with Nazism. Most supported the Weimar Republic. Mr. Weber's research shows that it's not really possible to connect the brutalization of men in the trenches to the birth of National Socialism.

It is very much to Mr. Weber's credit that he has managed to dig out the details, and we can place his book together with Ms. Hamann's as a triumph of original research in a very stony field. The conclusion that might be drawn is that Hitler was far more of the opportunist than is generally supposed. He made things up as he went along, including his own past. If we still haven't answered the question of what turned Hitler into an anti-Semitic idealogue, at least attention has been shifted to the Bavarian years of 1919-22. Ms. Hamann and Mr. Weber point the way forward for the next scholar's diligent researches.

Cheers, Nigel

"Ubique" - For the Royal Engineer it means 'Everywhere', For the Royal Artillery 'All over the place'.